Introduction

Climate change simulations are constrained by large uncertainties associated with aerosols. Progress has been slow, primarily as a result of temporal and spatial variability of tropospheric aerosols and our limited understanding of the multiple feedback processes involving aerosols. Potential impacts of aerosols on clouds and on the hydrological cycle constitute particular areas of concern. To quantify the global impact requires temporal information on concentration, size, composition, and altitude of aerosols on a global scale. For this purpose, dedicated regional field campaigns have been conducted (e.g., TARFOX, SAFARI, SCAR-B, ACE-Asia, AMMA) to study specific aerosol types, advanced sensors for extra detail and accuracy on aerosol properties have been placed on satellites, and ground-based aerosol monitoring stations have grown in number and equipment.

In the first part to this chapter, global maps of aerosol properties are provided that are also relevant to clouds. Beginning with the status quo of the last decade, recent advances in aerosol global modeling and aerosol remote sensing are presented. An overview of the major ground-based remote-sensing networks for aerosols is included, since this ground monitoring adds essential complementary detail and establishes a reference for remote sensing from space. The preferential use of statistics from these ground-based networks in combination with spatially complete data by global modeling yields new global monthly maps for aerosol properties. These maps include distributions of properties of anthropogenic aerosols and for CCN changes attributable to anthropogenic activity.

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